The subject matter of the invention relates to epoxy resin compositions and methods of balancing a rotor utilizing the same, and more particularly, to an ultraviolet light curable cross-linked epoxy resin composition and a method for dynamically balancing motor armatures and other rotors by dynamically testing the rotors repeatedly and applying an ultraviolet cured cross-linkable epoxy resin composition between tests to achieve the balance required.
Rotors such as electric motor armatures have previously been balanced utilizing a two-part epoxy based composition which is applied to an armature in a putty like consistency which is sufficiently tacky, adherent and cohesive to adhere to the armature during dynamic testing for balance prior to curing, dynamically testing the rotor with the balancing compound in position thereon, adjusting both the amount of the balancing position and the position of the balancing compound on the rotor to achieve the desired balance, and then curing the resin. See U.S. Pat. No. 3,939,020. This two-part epoxy composition includes one part which includes the epoxy resin and another part which includes the catalyst for curing the resin. Each part of the composition is stored separately from the other part until ready for use. When balancing is to be accomplished, the two parts of the composition are mixed in equal amounts by weight and the dynamic balancing of the armature is carried out by the method above-described. After desired balancing is achieved, the balancing compound can be cured either by allowing the armature to stand at room temperature for a period of time or heating the rotor.
Single part epoxy balancing compounds have also been proposed that have a shelf life of about three months at ambient temperatures. These balancing compounds can be utilized to balance motor armatures and other rotors in a similar manner as above described except that curing may be achieved within a range from about six minutes to about three hours at elevated temperatures, for example, 45 minutes at 300.degree. F. One example of these compositions are the BC motor balancing compounds by Star Technology, Inc.
Both of these prior balancing compounds require a large amount of energy or a large amount of time to cure the epoxy balancing composition. Some require both. In the balancing compound of U.S. Pat. No. 3,939,020, the balanced armature can be cured in about 20 minutes by heating the compound to a temperature of about 200.degree. F. In others, cure oven temperatures are used as high as 400.degree. F. for four hours. In some cases, these temperatures for prolonged times can cause the motor armature to distort and be once again out of balance or can cause another portion of the armature to thermally degrade. In the specific instance of armatures, the copper windings can expand and relocate upon curing to cause the armature to be again out of balance.
Prior balancing compounds are used in pieces or lumps, and it has always been a problem to thoroughly cure the balancing composition on the rotor in less than about four minutes. This is especially true with those balancing compounds which are heavily filled with mineral fillers which are applied to highly conductive metals such as those which predominate in a motor armature. It is believed that this lack of deep section cure is due to the temperature gradient between the outside of the piece or lump of balancing compound and the inside of the piece or lump normally experienced when oven curing these compounds on an armature of highly conductive metal. Some but not all of this deep cure problem can be overcome with catalysts.
Some manufacturers test armatures by spinning them at from about 2,000 rpm to about 15,000 rpm at elevated temperatures from about 250.degree. F. to about 300.degree. F. for about 30 seconds followed by balance tests. These spin tests show failures when the balancing compound is not fully cured, or when the heat deformation temperature of the compound is sufficiently lower than the test temperature.
It is therefore highly desirable to provide an improved balancing compound.
It is also highly desirable to provide an improved balancing compound which is a single part epoxy based composition which can be applied to an armature in either a paste-like consistency or a putty-like consistency.
It is also highly desirable to provide an improved balancing compound which can be provided in a single part epoxy compound which does not require mixing or formulation prior to use and has an appreciable shelf life.
It is also highly desirable to provide an improved balancing compound which can be cured rapidly at room temperature such that the balancing compound can be used on devices easily thermally degradable.
It is also highly desirable to provide an improved balancing compound which can be thoroughly cured by exposure to ultraviolet light and/or heat in a relatively short time.
It is also highly desirable to provide an improved balancing compound which remains in place upon the rotor during spin tests at elevated temperatures.
It is finally highly desirable to provide an improved balancing compound which has all of the features above mentioned.